Transepithelial Transport of Fluorescein in Caco-2 Cell Monolayers and Use of Such Transport inIn VitroEvaluation of Phenolic Acid Availability

Abstract

Fluorescein is a marker-dye customary applied to the evaluation of tight-junctional permeability of epithelial cell monolayers. However, the true mechanism for the permeation has not been elucidated. Transepithelial transport of fluorescein in Caco-2 cell monolayers was therefore examined. Fluorescein transport was dependent on pH, and in a vectorical way in the apical-basolateral direction, but it was independent of the tight-junctional permeability of monolayers of these human intestinal cells. The permeation of fluorescein was concentration-dependent and saturable; the Michaelis constant was 7.7 mM and the maximum velocity was 40.3 nmol min(-1) (mg protein)(-1). Benzoic acid competitively inhibited fluorescein transport, suggesting that fluorescein is transported by a monocarboxylic acid transporter (MCT). Antioxidative polyphenolic compounds such as ferulic acid from dietary sources, competitively inhibited the permeation of fluorescein. These compounds probably share a transport carrier with fluorescein. Measurement of the effects of phenolic acids on fluorescein transport across Caco-2 monolayers would be a useful way to evaluate the intestinal absorption or bioavailability of dietary phenolic acids.

Intestinal absorption of forsythoside A in in situ single-pass intestinal perfusion and in vitro Caco-2 cell models

“…This result is in good agreement with the distribution study and the results shown in Figure 4 and 5, showing that FTA was mainly permeated via paracellular diffusion. LY, a marker compound for paracellular transport, also showed this trend [24] . Figure 6 summarises the permeability coefficients of FTA in the absence and presence of inhibitors.…”

Transepithelial Permeability of Myricitrin and Its Degradation by Simulated Digestion in Human Intestinal Caco-2 Cell Monolayer

“…Small water-soluble molecules, such as water and lucifer yellow permeate the Caco-2 cell monolayer via the paracellular pathway. 11) To investigate the absorption route of myricitrin, we incubated the Caco-2 cell monolayer with various TEER values in a solution containing 100 mM of myricitrin and lucifer yellow in the apical side (Fig. 1).…”

Non-Involvement of the Human Monocarboxylic Acid Transporter 1 (MCT1) in the Transport of Phenolic Acid

“…17,19) MCTmediated transport of phenolic acids was first determined by this method. [4][5][6] The MCT isoform responsible for fluorescein transport is presumed to be identical to that responsible for the transport of phenolic acids in Caco-2 cells.…”

“…ferulic acid or p-coumaric acid) have shown lactic acid, which is a typical substrate for MCT1-MCT4, to have no effect on their transport. 4,5,17) Thus, it was tentatively proposed that Caco-2 intestinal cells might possess a novel MCT responsible for phenolic acid transport which is distinct from MCT1-MCT4. The results described in this paper confirm this proposal.…”

“…1C). However, the permeability of fluorescein, a known substrate of MCT in Caco-2 cells, 17) was unchanged after the treatment with NaBut (Fig. 1D).…”